PSMA Imaging Detects Prostate Cancer Spread

Correctly assessing prostate cancer’s spread is essential for staging and treatment options. Until now, scanning technology has lacked both clarity and specificity, leaving treatment recommendations to partial information and guesswork. The new PSMA PET scan changes this. This episode of PROSTATE PROS explores the benefits of the PSMA PET scan and how it can be used to make intelligent treatment decisions. READ MORE ABOUT ON OUR PROS BLOG.

Dr. Scholz:      [00:03] We’re guiding you to treatment success and avoiding prostate cancer pitfalls.  I’m your host, Dr. Mark Scholz.

Liz:      [00:09] And I'm your cohost, Liz Graves. 

Dr. Scholz:     [00:13] Welcome to the PROSTATE PROS podcast. 

Liz:      [00:17] Prostate cancer imaging has improved tremendously over the last decade. Advanced imaging means safer screening, more accurate staging, monitoring, and targeting. 

Dr. Scholz:      [00:29] Liz, I'm glad we're going to address this new area of prostate cancer imaging because there's one scan in particular called PSMA PET scan, which is revolutionizing the field. 

Liz:      [00:42] So PSMA stands for prostate specific membrane antigen.  This is a scan that I hear you talk about all of the time in the office.  Can you tell us what it does? 

Dr. Scholz:      [00:55] Whenever we're talking about scans we're always trying to answer the $64,000 question: Where is the cancer?  The scary thing about cancer is it can spread and with prostate cancer, of course, ideally we want the cancer to stay confined inside the prostate gland.  Historically, we've had a variety of scans to look throughout the body, MRI scans, bone scans.  The problem has been that these scans are nonspecific, they can light up with injuries and other cancers and all kinds of confusing things. And they're not really that accurate so they can miss cancers outside the prostate, even when they're there. 

Liz:      [01:37] PSMA only shows where the prostate cancer is located in the body. 

Dr. Scholz:      [01:43] That's right.  And let's reiterate, of course, that prostate cancer that spreads to a lymph node or to the bones doesn't become bone or lymph node cancer, it's still prostate cancer. And the PSMA signature stays intact, even if it gets into another part of the body.  So if a spot lights up on the scan, this new PSMA PET scan that we're talking about, it means there's some prostate cancer there. 

Liz:      [02:09] I'd imagine this is really important for staging.  Right now you are using a lot of different ways to predict if the cancer has spread, but with this PSMA scan, you'll know for sure. 

Dr. Scholz:      [02:22] That's very well stated.  The historical use of Gleason Score was to try and predict the likelihood of something being outside the prostate or how high the PSA is.  High PSAs were statistically more likely.  This scan is so much more accurate than anything we've had.  Now, if the scan is negative, it doesn't entirely prove there's no cancer outside the prostate, but it gives us a lot more confidence that the cancer is still confined inside the gland.

Liz:      [02:50] The scan seems pretty revolutionary, is everybody getting this?

Dr. Scholz:      [02:55] PSMA PET scans are available in a number of research centers, university centers around the country right now.  And they are usually associated with some sort of a financial charge, but the information is so valuable, the money is usually dollars well spent. 

Liz:      [03:13] Besides having enough money to afford the scan who's eligible, is it every stage?

Dr. Scholz:      [03:19] It is almost every stage.  The exception would be men with what we call SKY or Low-Risk prostate cancers, MRIs are more accurate for delineating the exact size of spots inside the prostate, but for pretty much every other stage this is the best scan experience has shown that men with PSS that are below 0.2 are not going to light up on the scan.  That’s a pretty remarkable threshold because with older scans, people needed PSAs of one to two, with something like Axumin perhaps, or 10 to 20, if it was a regular bone scan. 

Liz:      [04:00] So you mentioned Low-Risk, and these are cancers that as far as we know, haven't spread, is there a situation where these men would want to get a PSMA scan? 

Dr. Scholz:      [04:11] You know, I have used it.  That's not normally the way we would use the scan, but there's a situation where men are thought to have SKY, Grade 6, prostate cancer, but many times we run into men that have high PSA levels, perhaps from prostatitis or big prostates.  There's this nervous niggling concern that could the cancer have spread somewhere outside the prostate.  So it brings a lot of comfort when you have a high powered scan like this into play and show that no, indeed it is only still in the prostate.  So while we don't routinely use this type of scanning, the PSMA PET scan for men with localized disease, certain men that are running high PSA density, that means the PSA is higher than we would expect in regard to how big the prostate is.  We might consider doing a PSMA PET scan, and we have done that in a few cases. 

Liz:      [05:06] So let's say one of these men does want a PSMA PET scan before that because they have local disease.  They would probably have had a 3T mp MRI or a color Doppler ultrasound. 

Dr. Scholz:      [05:20] Yes, exactly.  So we have literally hundreds of men we're monitoring on active surveillance.  Our typical policy is to do imaging with 3T multiparametric MRI and/or color Doppler ultrasound.  These provide the greatest resolution for imaging inside the prostate gland.  So if a person's previously had a biopsy and we know where the cancer is and what the grade is, and they're under surveillance, sequential scanning can determine if those spots are growing. And so that is how we determine if someone will need further biopsies.  Secondarily, we do look at PSA, but PSA is just not very accurate for this sort of purpose. 

Liz:      [06:03] We talked about Low-Risk, but how does this new scan help men with High-Risk prostate cancer? 

Dr. Scholz:      [06:10] So what High-Risk means, and it's good to define terms, it doesn't mean a High-Risk of dying, it means a higher risk of microscopic spread outside the gland so that men who would undergo surgery or radiation would be at a higher risk of not being cured.  So to compensate for that doctors give men TIP or testosterone inactivating pharmaceuticals, androgen deprivation, to try and mop up those little specks that might be out there just because someone has a higher Gleason Score or a higher PSA, but this scan is so much more accurate.  It raises the question: If the scan doesn't show any spread can men with High-Risk disease skip taking the testosterone blockade and simply monitor with sequential scans annually after the treatment?  And if some little tiny speck shows up in the future then treat it with radiation and perhaps some hormone therapy at that point.  This would be a wonderful advantage for men because as we all know, four to 18 months of testosterone blockade is a very onerous treatment with a lot of side effects.  So these scans may enable men to either reduce or eliminate the testosterone blockade. 

Liz:      [07:24] You just mentioned sequential scanning.  How often would you do that for someone with the PSMA scan? 

Dr. Scholz:      [07:30] So if someone has High-Risk disease and they're in complete remission, it would probably depend on how High-Risk, but it's funny how often in the scanning world, like for instance, with SKY, we do MRIs once a year, color Doppler once a year, and annual follow up is sort of a common rhythm.  Unfortunately, we don't have any studies yet to tell us what is going to be the optimal scanning period. 

Liz:      [07:56] I know that a lot of scans have a lot of radiation or you have to use contrast.  And these are a couple of things that can make it a little messy when considering getting a lot of scans in a row, is that something people need to be worried about?

Dr. Scholz:      [08:10] It could be.  The contrast or the radiation exposure does incur a small risk.  Of course, in men with sky cancers, doing a lot of scanning that has radioactivity would be inappropriate, but as people get higher risk cancers, of course the disease itself becomes more risky than the side effects of the radiation. 

Liz:      [08:31] We've been talking about a lot of applications for this, but the most common application is finding relapsed disease. 

Dr. Scholz:      [08:40] Exactly.  So people that have had surgery or radiation, their PSA should go down to very low levels and remain there indefinitely.  But PSA relapse is really common about 25% to 35% of men will have a rising after surgery or radiation someday.  Then the big question is, well, where's it coming from?  In the past, we really just had to deal with guesswork.  There is another type of scan called Axumin, which is FDA approved, which was definitely progress because when the PSA got to be around one, two, or three oftentimes it was possible to find the location of the cancer.  What’s marvelous about the PSMA PET scan is you can start scanning when the PSA is as low as 0.2. 

Liz:      [09:27] So I would imagine if something's found that relapsed disease is happening and there are mets that you can start treatment right away. 

Dr. Scholz:      [09:36] Yes.  And it's directed treatment.  Usually the problem is located in the pelvic lymph nodes.  That's the first jumping off spot.  The doctors, now with modern radiation, can safely zap those spots and people get a second chance for cure. 

Liz:      [09:53] Moving on to men with advanced prostate cancer.  These are men that have mets outside the lymph nodes and maybe even in the bones.  So in the past, these men had to get all sorts of scans.  They had to get bone scans, CT scans, but now with the PSMA PET scan, they might only have to get this one scan. 

Dr. Scholz:     [10:16] I think that's a great advantage with these scans, but in addition, of course, this is even more accurate.  So if the CAT scan showed one or two enlarged lymph nodes and the bone scan showed one or two spots, the PSMA PET scan is so much more powerful and accurate, it may reveal significant numbers of new spots that weren't seen on the old scans. 

Liz:     [10:42] How is that helpful?                                    

Dr. Scholz:      [10:45] Well, treatment is tailored to how many spots are present because if only two or three spots are present, you can zap them with beams of radiation and try and sterilize them.  But if there's a myriad of spots out there, medicines that circulate through the bloodstream, hormone therapy, chemotherapy, immunotherapy, is the best way to go. 

Liz:      [11:07] So the PSMA PET scan can be used for people with all different stages, and it can really help guide treatment and stage patients.  Dr. Scholz, it seems like almost every person with prostate cancer should get this scan, but it's only approved in other countries, why is that?

Dr. Scholz:      [11:26] There's been a lag in the United States with the completion of the clinical trials. And I'm not sure exactly why.  This technology was actually invented 20 years ago.  A guy named Neil Bander came up with a PSMA antigen and thank God now fruition is near.  The studies have been completed and we're waiting for them to break the code and render proof that these scans are actually as good as we're talking about.  And we know that they will be.  Once the code is broken and the studies are published, there's usually a three to six month delay until the FDA approves the scans for commercial use. 

Liz:      [12:04] So for now finding PSMA PET scans is usually at a university or through a clinical trial. 

Dr. Scholz:      [12:12] Yes.  And unfortunately it's associated with a charge sometimes $1,000 to $3,000 per scan.  They're pretty pricey, but I've found that the information has been so useful that many patients are willing to invest the dollars necessary to get the information. 

Liz:      [12:30] Let's say someone doesn't have the resources or the money to get a PSMA PET scan. What are these people supposed to do?  

Dr. Scholz:      [12:37] Well, we've been getting by without PSMA PET scans for 20 or 30 years and the PET bone scans, the Axumin PET scans, and good high quality MRIs have enabled us to improve prostate care to a tremendous degree.  The PSMA PET scan is definitely an advance.  In fact, I've been billing it as the biggest discovery since PSA, but it is the way we've been practicing without PSMA PET scans is certainly viable.  And with expert care, doctors can use these slightly inferior technologies to make reasonable decisions and gage what the best approach will be. 

Liz:      [13:20] So this is a really exciting topic, and we are a little early talking about it as it isn't FDA approved yet, but it will be soon.  We're posting more information about it on our blog, prostateoncology.com/blog.  We're really excited to keep you up on the latest in prostate cancer.  You can email any questions or topics to [email protected].  Remember to help us out by rating, reviewing, and subscribing on Apple Podcasts.